Developmental studies of visual information-processing have con- sistently shown that young children do not differ from adults in attention, processing speed or memory in tasks employing presentation of a single item. Nevertheless when multiple-item arrays of information are employed, strong age differences in these processes have been observed. The present proposal is an attempt to explain these age trends within a theory of attention based on a notion of a limited processing capacity. It is proposed that developmental differences in selected information-processing tasks are a function of the amount of effort or processing capacity required by different age groups to alert to, encode, remember and organize stimulus information. A series of five studies employing tachistoscopic procedures will explore this notion with a view to distinguishing those processes which require significant amounts of effort or capacity from those which do not.